Force-feedback technology and related devices may be divided into four broad application areas: medical, entertainment, teleoperations, and virtual reality. Teleoperations, the research of which provided the foundation for the development of force-feedback devices, is the process of locally controlling a remote device. The primary difference between virtual reality and teleoperations is in the objects which they control. With teleoperations, actual physical robots are manipulated in the real world, whereas virtual reality involves simulated devices in synthetic worlds. Force-feedback for telerobotics has evolved large and bulky mechanical arms to more joystick-like designs. In general, these devices are designed for six degree-of-freedom (6DOF) force feedback, and have the capability to provide high levels of force. More recently, finger-operated devices have also been introduced for use in teleoperations applications.
The use of force feedback in medical training, simulation, and teleoperations is also increasing, with the primary application being minimally invasive surgical techniques which use laparscopic tools to perform intricate tasks when inserted into body cavities through small incisions. To realistically simulate laparoscopic tool forces, special-purpose force-feedback devices are currently under development.
The entertainment field is very difficult to address with force-feedback technology, since the applications demand both higher performance and lower costs. There are three primary markets for force feedback devices in entertainment: location-based entertainment (LBE), arcades, and home entertainment. LBE demands the highest performance while home entertainment demands the lowest cost. Despite the conflicting demands, progress is being made in each of these fields.
It may be argued that each of the application domains just described has its roots in virtual reality, which is becoming dominant in all immersive applications. As a consequence, on-going research in immersive applications is often termed “virtual reality,” whereas, when the research is completed, the application is given a specific name, such as a surgical simulator. Overall, virtual reality is becoming increasingly popular as a preferred means of interacting with many scientific and engineering applications. To cite two of many examples, molecular modeling and automobile design are moving from standard graphics, carried out on conventional graphics terminals, to more interactive environments utilizing 3-D stereo graphics, head-mounted displays and force feedback.
As visualization is a very important aspect of these applications, interesting and useful technologies are being developed, including graphical object representations and large working volumes (CAVES). Concurrently, haptic interfaces are being perfected, which enable manual interactions with virtual environments or teleoperated remote systems. The haptic system is a unique sensory system in that it can both sense the environment and allow a user to react accordingly. As a result, haptic devices not only stimulate the user with realistic sensor input (forces, tactile sensations, heat, slip, etc.), but also sense the user's actions so that realistic sensory inputs can be generated. Haptic devices are divided into two classes, depending upon the type of sensory information being simulated. The first, tactile, refers to the sense of contact with the object. The second, kinesthetic, refers to the sense of position and motion of a user's limbs along with associated forces.
Broadly, these approaches point toward the same goal: to immerse a person in a seemingly visual reality, complete with haptic feedback. However, a major deficiency with all existing force-generating devices is the requirement that they be connected to a fixed frame, thus forcing immobility on the user. State-of-the-art force-feedback devices, for example, are table mounted, requiring the device to be mounted to an immobile object in order to generate a fixed point of leverage for forces and/or torques. Consequently, no existing force feedback device allows for easy mobility and force generation. This problem is fundamental, since many virtual reality applications require large working volumes and the ability to move freely within these volumes, to provide realistic visual and audio feedback during walk-through scenarios, for example.
In summary, large, immersive environments such as CAVES currently lack haptic feedback, primarily because the existing technology will not support unrestricted motion. This leads to one conclusion that force-feedback devices must migrate as visual technologies have, that is, from the desktop to large-volume, immersive environments. However, the design of a hand-held, spatially unrestricted force-feedback device is fundamentally different from existing devices, which typically use primarily electromechanical or pneumatic actuators operating against fixed supports to achieve active force feedback. Nor is the realization of such a device intuitively obvious. To construct an n-axis joystick, requiring 1, 2, 3 to n+3 motors, presents significant challenges, for example, since the additional motors may significantly increase the cost and/or weight of the device.